Alternating Polarity Rotor Windings for Parasitic Current Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In electric motors, particularly separately excited synchronous motors, parasitic currents due to stray capacitance between the rotor winding and the rotor body or shaft result in undesired energy losses and potential damage, which existing bearing protection devices only partially address.
Innovation Solution
A rotor design with an even number of pole pairs connected in series, where the polarity of consecutive rotor windings alternates, and the current flow direction through the windings is optimized to reduce capacitive coupling, with symmetrical sections of the series circuit to cancel out stray currents and minimize capacitive coupling effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If rotor windings are connected in series with alternating polarity, then parasitic currents are reduced, but device complexity increases
Solution Approach 1:
The rotor windings are configured with alternating polarity in series connection, creating an asymmetric current distribution pattern that causes parasitic currents in different sections to oppose each other. This asymmetric arrangement reduces the net parasitic current flow through the rotor body and shaft, thereby reducing energy losses while maintaining a manageable structural complexity through systematic winding design.
2Reliability
If bearing protection devices are added to ground the rotor shaft, then bearing damage is prevented, but device complexity increases
Solution Approach 1:
Instead of adding bearing protection devices to prevent harm, the invention converts the potentially harmful parasitic currents into a beneficial self-canceling phenomenon. By configuring the rotor windings with alternating polarity, the parasitic currents generated in different sections flow in opposite directions through the rotor body and shaft, naturally neutralizing each other and eliminating the need for additional protection components.
3Strength
If rotor body and shaft are made of electrically conductive material, then mechanical strength is improved, but parasitic currents are generated
Solution Approach 1:
The invention maintains the electrically conductive material for the rotor body and shaft to ensure mechanical strength, but applies a specific winding configuration that creates localized current patterns. The alternating polarity arrangement ensures that parasitic currents are generated in a controlled manner in different sections, causing them to oppose and cancel each other, thus eliminating harmful effects while preserving the beneficial mechanical properties of conductive materials.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design significantly reduces parasitic currents and associated energy losses, enhancing electromagnetic compatibility (EMC) and extending the lifespan of the rotor shaft and its bearing by minimizing capacitive coupling between the rotor winding and the rotor body or shaft.
Implementation Method 1
The energy made available by the magnetic interaction between the stator and the rotor can be tapped via a rotor shaft
Implementation Method 2
stray capacitances being able to occur between the rotor body and the rotor shaft and secondly the at least one rotor winding surrounding it so that parasitic currents can result
Data Source
AI summary
A rotor for an electric motor includes an even number n of pole pairs arranged on a rotor body with rotor windings connected in series between two electrical connections to supply or conduct away current through the rotor windings. The series circuit has a first section including n/2 rotor windings arranged first in the series circuit, and a second section including n/2 rotor windings and arranged upstream of the second electrical connection. During application of a direct-current voltage between the two connections in each of the rotor windings of the first section, the radial component of the direct-current flow in the series circuit extends through the entire respective rotor winding, from an outer side to an inner side of the rotor winding, and in each of the rotor windings of the second section, in reverse, from an outer side to an inner side of the rotor winding.